American winged rocketplane. NASA-sponsored suborbital unmanned prototype for a single-stage-to-orbit rocketplane. The Lockheed Martin vehicle would have used a linear aerospike engine, metallic insulation, and other features similar to their Starclipper shuttle proposal of 1971. In 1999 catastrophic failure of the composite fuel tank during static test brought into question the technical feasiblity of the design. The program was cancelled in 2001 before any flight articles were completed and after over $1.2 billion had been expended.

NASA began the X-33 program in 1996 as part of its Reusable Launch Vehicle program. It called for the demonstration of a subscale single-stage-to-orbit vehicle. Five companies expressed interest and submitted concepts. Three teams were selected to provide final proposals for half-scale suborbital prototypes of full-scale vehicles:

Lockheed, by then Lockheed Martin Corporation, was selected. By 5 March 1999 airframe components had been fabricated, engine stand tests were under way, structural tests had begun, and NASA dedicated the $32 million, 30-acre X-33 Flight Operations Center at Edwards Air Force Base. The center was designed the X-33 to be serviced and launched from that single location with a ground crew of fewer than 50 people. Two seven-day turnarounds and one two-day turnaround was planned to be demonstrated during the X-33 flight test series.

Using composite materials to reduce vehicle weight was considered one of the keys to successfully developing a single-stage-to-orbit vehicle. In November 1999 the X-33's composite liquid hydrogen fuel tank failed during testing. An investigation into the cause of the failure revealed that composite technology was not mature enough for such use in cryogenic reusable tanks. Lockheed Martin proposed to complete development of the X-33 by replacing its two composite liquid hydrogen tanks with aluminum tanks. But NASA decided that the benefits of testing the X-33 in suborbital flight without proving the critical composite technology did not justify the cost.

NASA investment in the X-33 program totaled $912 million. Lockheed Martin originally committed to invest $212 million in the X-33, and during the life of the program increased that amount to $357 million. For that money NASA and Lockheed Martin essentially proved that rocket-powered / vertical-takeoff / horizontal-landing single-stage-to-orbit vehicles were not feasible using existing technology. The result essentially killed further consideration of single-stage-to-orbit designs in America, Europe, and China for decades to come.

RS-2200 Rocketdyne lox/lh2 rocket engine. 2201 kN. Development cancelled 1999. Isp=455s. Linear Aerospike Engine developed for use on the Lockheed Reusable Launch Vehicle, the production follow-on to the X-33. More...

Winged In the beginning, nobody (except Jules Verne) thought anybody would be travelling to space and back in ballistic cannon balls. The only proper way for a space voyager to return to earth was at the controls of a real winged airplane. More...